madbeanpedals::forum

Projects => How Do I? Beginner's Paradise. => Topic started by: helos on September 10, 2018, 01:06:11 AM

Title: Led Popping noise
Post by: helos on September 10, 2018, 01:06:11 AM
Hello guys, I hope you can help me!

I wanted to improve my use of Eagle and I had some PCB fabricated for a compressor circuit.
The effect works well except for a little pop noise (actually it's more a "tick" than a "pop") when I switch on the effect.

I'm sure it's the LED, because if I disconnect it from the ground (so that it doesn't light up) there's no noise at all...

I also tried to add a cap and other limiting resistor as shown on Muzique website, but nothing changes...

I'm using a high brightness white led with a 15k limiting resistor tied directly to 9v dc jack (before the diode polarity protection). The negative side of the led is tied to the 3pdt.

I'm wondering if the size of the 9v and ground traces (that go to/from the LED) are somehow related to this... actually the size is 10mils for the ground trace and 15 mils for the 9v.

Could it be due to the LED quality? I used one from China... not the best source I admit...
If so, what LED would you suggest me?

Can someone help me?

Thank you very much!
Title: Re: Led Popping noise
Post by: drog_trog on September 10, 2018, 02:44:27 AM
Which circuit is it
Title: Re: Led Popping noise
Post by: helos on September 10, 2018, 03:57:00 AM
An optical ocmpressor by craig anderton found online...
Title: Re: Led Popping noise
Post by: drog_trog on September 10, 2018, 06:43:05 AM
Looking at the schematic there is 100k between output and ground so maybe increase that to 1M
Title: Re: Led Popping noise
Post by: helos on September 10, 2018, 07:26:25 AM
Looking at the schematic there is 100k between output and ground so maybe increase that to 1M

I'm pretty sure it's not about pulldown resistors: there's no parasitic voltage at the output... Infact, if I disconnect the led, there's no noise at all when I press the switch... It must be the led.

I was wondering that maybe it could be due to the size of the ground trace coming from the led to the 3pdt
Title: Re: Led Popping noise
Post by: drog_trog on September 10, 2018, 09:04:46 AM
ok, maybe try a different led brand, what size traces do you use
Title: Re: Led Popping noise
Post by: madbean on September 10, 2018, 10:25:36 AM
Here's a little trick that might come in handy if you can't get rid of the popping. It uses a BJT as a switch to turn the LED on a bit more slowly. When the SW connection is closed, current is applied to Q1 base according to the time constant set by the 100k/10uF combo (a second or less @9v). You can increase the time it takes by increasing the value of the 10uF (say 47uF or 100uF).
Title: Re: Led Popping noise
Post by: helos on September 11, 2018, 01:33:30 AM
Here's a little trick that might come in handy if you can't get rid of the popping. It uses a BJT as a switch to turn the LED on a bit more slowly. When the SW connection is closed, current is applied to Q1 base according to the time constant set by the 100k/10uF combo (a second or less @9v). You can increase the time it takes by increasing the value of the 10uF (say 47uF or 100uF).

Great!! Thanks! I'll try it!
Title: Re: Led Popping noise
Post by: peterc on September 11, 2018, 03:00:14 AM
Couple of things to try:

Increase the value of the LED resistor to decrease the current flowing through the LED. Increase the value until the LED dims, and then go back one value. Idea is to get the LED to use as little current as is needed for it to work.

My other suggestion is to put a 100nF cap across the LED or even a 10uF. This may work.....
Oddly it worked for me once but on another occasion it did not. Go figure...

Good luck